This invention relates to error detectors and more particularly to error detectors for pulse signals which alternately extend in opposite directions.
Telephone systems have what are referred to as span lines for transmitting a T-type carrier between central offices. The span line has a bipolar pulse train in a four wire configuration. One pair of wires are for transmitting and one pair are for receiving the T-type carrier.
It has been found that errors occur in the transmitting equipment for the T-type carrier. When the transmitter is operating correctly, a T carrier always has a positive pulse following a negative pulse and always has a negative pulse following a positive pulse. If the pulses do not alternate between positive and negative on successive pulses, an error is occurring and must be detected promptly for service or repair.
Test sets exist for detecting errors in the T carrier. However, known test sets are complicated, expensive and require adjustments such as by a switch. One device requires a switch to switch the test set to one state to monitor the T carrier for errors and to switch the test set to another state for monitoring the T carrier for merely the presence of pulses.